import java.util.Scanner;

public class test1 {
    public static void main(String[] args) {
        //用递归计算1 + 2 + 3 + 。。。+ 10
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        System.out.println(add(n));
    }
    public static int add(int n) {
        if (n == 1) {
            return 1;
        }
        return n + add(n - 1);
    }
}
